Reversible Bus Pair

Discussion in 'The Projects Forum' started by mbxs3, Apr 5, 2011.

  1. mbxs3

    Thread Starter Active Member

    Oct 14, 2009
    141
    3
    I didn't want to piggy back off another thread so here is my inquiry...

    I was hoping someone could explain to me how a reversible bus pair works as seen in the schematic in this thread:

    http://forum.allaboutcircuits.com/showthread.php?t=52502&page=2

    This circuit was posted by BillB3857 based off CitrPug's originally posted schematic.

    I am just used to a designated power input or rail and a ground rail so I am looking for a break down of what is occurring here. I am not concerned with the rest of the schematic. Any input will be greatly appreciated. Thanks.
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    In a reversible bus pair, the two lines take turns. In the example shown, lets say that for the LOCK condition, the left side is +12 and the right side is ground. That would energize the left side relay. For the UNLOCK condition, the left side would be ground and the right side would become +12. In that case, the right side relay would energize. The two wires at the far right, labeled To Mirror Motor, are what I call a reversible pair. Very common usage in automobiles to reverse small DC motors such as window up/down, door lock/unlock, mirror up/down, left/right, etc. Of course to cause no motion, both would be at the same potential. In my diagram, they would be both ground feeding the mirror motor.
     
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  3. mbxs3

    Thread Starter Active Member

    Oct 14, 2009
    141
    3
    Thanks for the breakdown!
     
  4. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    A lot can be done with diodes. One of the problems given when I first started to learn electronics was to devise a circuit that had two lights at one end of a room and two switches at the other end. How do you make Switch A turn only Light A on, Switch B turn only Light B on with only two wires running between the switch pair and the light pair. Power was a 6.3 volt filament transformer.
     
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